When a disc brake apparatus is used to hold a rotating body in industrial machinery and the like, in a negative type disc brake apparatus which uses the load of a disc spring directly as a braking force, there is generally known an apparatus which uses a hydraulic force to release the braking force. However, the system of the whole of the negative type disc brake apparatus is desired to exclude space and piping for employment of a hydraulic mechanism to thereby realize miniaturization and simplification.
In the negative type disc brake apparatus, as a method for applying a force to a piston using other means than the hydraulic mechanism, there is known a technology using a cam as disclosed in the patent document 2 and patent document 3. In a disc brake apparatus disclosed in the patent document 2, there is employed a structure in which an eccentric cam shaft is arranged in a penetration hole formed in the side surface of a piston and, when the eccentric cam shaft is rotated, a pressing force is applied to the piston. In a disc brake apparatus disclosed in the patent document 3, there is employed a structure in which a cam lever is arranged on the rear end of a piston and, when the cam lever is rotated, the piston is pushed out to thereby apply a pressing force to the piston.